I have a 93 f-150 with 300 - 6cyl and M50D 5-spd.
It has 106K and went through a alternator at about 60K and another at 80K. I've replaced the starter and the positive batt cable. Here's my problem. My ignition switch no longer seems to have any detents. When I park, I have to position it so the chimes will stop. It works; it starts and stops the engine, but goes from acc to off to on without hitting any stops or detents. After driving it like this for 15K or so, I'm now noticing that my wiper motor is getting loud and slow, and my electric windows are sluggish. Seems like my lights may be dimmer too but I'm not certain since this all happened gradually. Also, my intermittant wipers seem to have lost all there intermittant speeds. I have the very slowest one, and the then just hi and low. It's like the whole electrical system is getting tired and slow. Any ideas?

 

Install a voltmeter so you will know if the alternator is working properly. You just have to fix the bad systems one at a time.

 

You never mentioned that you replaced your battery. A dead or barely kicking battery will give you all the symptoms you listed with the other electrical circuits.

 

The detents are built into the switch, so replace it. You can see where it is by looking at pic #23 in this photo album. A poor contact could cause your symptoms by high resistance to switched circuits.

 

The battery is relatively new and there are no problems with starting.